Can Second Hand Weed Smoke Cause a Failed Drug Test?


I have a lot of friends that do not consume marijuana. Sometimes it is because the person simply does not like marijuana, but more often than not it is due to some type of drug testing requirement that they face. It can be because the person is on probation, or most likely because of the person’s job. Random drug testing is an unfortunate reality for many people I know.

A very common question that I get from friends is whether or not they can test positive for marijuana just for being around someone who is smoking it. It’s a valid question, especially if they hang around me (I smoke like a broken chimney). For the most part, people have nothing to worry about when being around someone consuming marijuana if it’s in a well ventilated area. But if the person is in a confined area for a long period of time, perhaps as a bystander in a ‘hot box’ scenario, it’s very possible for that person to test positive for marijuana.

What The Science Says

A study from 2015 put people in a specially built room for one hour surrounded by six people who were smoking marijuana with a THC level of 11.3%. The study involved the specially constructed room/chamber either having no ventilation at all (hot box style) and a room with partial ventilation so that the air circulated 11 times per hour. Below is what the study concluded:

Exposure to secondhand cannabis smoke under unventilated conditions produced detectable cannabinoid levels in blood and urine, minor increases in heart rate, mild to moderate self-reported sedative drug effects, and impaired performance on the digit symbol substitution task (DSST). One urine specimen tested positive at using a 50 ng/ml cut-off and several specimens were positive at 20 ng/ml. Exposure under ventilated conditions resulted in much lower blood cannabinoid levels, and did not produce sedative drug effects, impairments in performance, or positive urine screen results.

The big takeaway from the study, other than that someone can test positive after hot boxing with friends, is that ventilation matters. If someone is on a porch around a friend who is smoking a joint, they have nothing to worry about. But if they are in a small room with a group of friends that are smoking down hard, they definitely run the risk of failing a drug test. Part of being a responsible marijuana consumer is respecting other people’s situation, so if you have a friend or loved one that really needs their job (or freedom in the case of probation), be mindful of this study and let them know that they should probably just wait outside while you are hot boxing, or take your consumption to a well ventilated area.

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